This invention relates to diaphragms for such uses as air-operated or mechanically operated diaphragm pumps, brake actuators or other diaphragm-operated devices in which a central plate or plates is connected to or makes contact with the central portion of the diaphragm.
Pump diaphragms have traditionally been made of fabric reinforced rubber, typically having a relatively thick and constant wall thickness of usually about 0.125 inches to about 0.320 inches. The wall thickness is usually in the range from about 1.2% to about 3% of the outside diameter of the flexure portion of the diaphragm. An example of the conventional rubber diaphragm is shown is U.S. Pat. No. 3,911.796 to Hull et al. Diaphragms of this type are generally dish shaped, having a top planar portion which undergoes the greatest amount of abrasion and wear, an outer flange portion which may be dovetailed or beaded for retention in an associated pump housing, and an innerconnecting flexure sidewall portion. Fabric reinforcement must be embedded in the body of these diaphragms to achieve adequate flex fatigue life, which drives up the cost. Rubber diaphragms also require use of a relatively large quantity of material because a thick wall is needed for abrasion resistance and to meet flexing requirements. In certain applications the lack of chemical resistance presents problems as well.
To a limited extent, plastic materials with relatively stiff central portions and thinner, more flexible sidewall portions have been used in some diaphragm applications, for instance, as disclosed in U.S. Pat. No. 3,011,758 to McFarland, Jr. Thermoplastic polyurethane diaphragms have also been used as pump diaphragms. These polyurethane diaphragms have been constructed with a generally curvilinear flexure sidewall incorporating concentric ribs, terminating in an outer beaded flange and radially inward bead for mounting to a split piston plate. The sidewall thickness of these polyurethane diaphragms has been from 0.090 inches up to 0.250 inches. Alternately, the sidewall thickness of these polyurethane diaphragms has been from 1% to 3% of the outside diameter of the flexure portion of the diaphragm.
Two primary modes of failure for pump diaphragms, particularly of the thermoplastic type, are abrasion failure due to the diaphragm contacting the piston plates and the pump housing areas immediately adjacent to where the diaphragm is clamped to the housing, and fatigue failure due to repeated flexing. Abrasion life is maximized normally by increasing material thickness, while flex life is normally maximized by decreasing material thickness. These competing requirements present a problem which is accentuated with nonreinforced, thermoplastic diaphragms.
It is a primary object of this invention to provide a diaphragm made of a nonreinforced thermoplastic material which has an acceptably long flex life and superior abrasion resistance.
It is another object to produce such a diaphragm by proper design of wall thickness and contour to minimize use of material and cost without sacrificing the life of the diaphragm.
In addition to the foregoing statement of the prior art, the following patents are considered relevant to this invention: U.S. Pat. Nos. 3,680,981 to Wagner; 2,904,068 to St. Clair; and 4,238,992 to Tuck, Jr.